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Most of efforts have been made to prepare high performance surface-enhanced Raman scattering (SERS) substrate for amplifying Raman signals. It still remains a grand challenging task in building a simple, conventional and low-cost SERS substrate with highly dense hotspots for improved sensitivity of the target analytes. Here, we report a very dexterous strategy to fabricate a distinctive SERS substrate with high density hotspots, using common adsorbent activated carbon (AC) as template to assemble silver nanoparticles (Ag NPs). It can be estimated that the enhancement effect of Ag NPs/AC composite is about 6.5-fold that of bare Ag NPs. Different from the resonant dyes, however, formaldehyde (FA) is a Raman-inactive molecule even though enhanced. Considering that, a novel method for quantitative analysis of FA using the Ag NPs/AC composite as SERS sensor has been developed, based on the catalytic effect of trace FA on the oxidation of malachite green (MG) through bromate under acidic condition. The change of MG from reduced form into oxidized leucomalachite green (LMG) results in the quench of Raman signals of MG, responding to 0.07 ppb FA that is about 2 orders of magnitude lower than the limit defined by the Nash's method as a standard procedure recommended in Europe, Japan and China. Moreover, SERS examinations of endogenous FA in human urine signify that the proposed method has high selectivity, reliability and accuracy. Thus, as-fabricated Ag NPs/AC composite is adequate as inexpensive and versatile SERS sensor utilized in the quantification of trace targets in various complicated matrices. [ABSTRACT FROM AUTHOR]

Abstract: For the widely used gold nanoparticles (AuNPs)-based colorimetric probes, AuNPs generally change from dispersion to aggregation state accompanying with corresponding color turning from red to blue. Although colorimetric probes based on the anti-aggregation of AuNPs show exceptional selectivity and sensitivity, few examples have been reported in literature. A facile but highly sensitive and selective colorimetric probe based on the anti-aggregation of AuNPs transferred from the deactivation of aggregation agent 4,4′-dipyridyl by Hg2+ was developed in this work. This reported probe is suitable for real-time detection of Hg2+ in water with a detection limit of 3.0ppb for Hg2+, and exhibits a selectivity toward Hg2+ by two orders of magnitude over other metal ions. The dynamic range of this probe can be conveniently tuned by adjusting the amount of 4,4′-dipyridyl used. [Copyright &y& Elsevier]